1. Field of the Invention
The present invention relates to a method for checking the operability of a vehicle safety system for activating a vehicular safety device such as an inflatable air bag or a safety belt tensioning device at the time of the occurrence of a collision of a vehicle to protect the driver and/or passenger(s).
2. Description of the Prior Art
The conventional safety system of this type is arranged to detect the sudden deceleration occurring at the time of vehicle collision on the basis of the integrated value of the vehicle acceleration detected by an acceleration sensor and to activate the safety device when the magnitude of the sudden deceleration has reached a prescribed level. Consequently, it is necessary for the safety system to ensure both the detection of the occurrence of the predetermined deceleration state produced by the vehicle collision and the activation of the safety device. Furthermore, it is also preferable for the system to constantly check the operability of the safety system during the running of the vehicle and to inform the driver of the result when the safety system has malfunctioned.
One example of an arrangement for realizing the foregoing requirements is disclosed in Japanese Patent Application Public Disclosure No. Sho 63-241467 (corresponding to U.S. Pat. No. 4,950,914) which describes a vehicle collision detection device having a self-check circuit. In this device a test pulse signal generator is operated to apply a test pulse to a piezo-electric element of the acceleration sensor for detecting impacts caused by vehicle collisions and it is checked whether or not a predetermined output signal is obtained at the output of the signal processing circuit for processing the output signal from the sensor in response to the application of the test pulse. However, this arrangement is not capable of checking the operability of the firing element.